Tuesday, February 7, 2012

FYP in My Style : McFarland Standard

Okay since I already done this quite for a long time so I think it is okay for me to write something about McFarland standard.
Almost all of my friends whom doing antimicrobial test will do McFarland Standard before proceeding. What is actually McFarland standard? Based on keyscientific, McFarland standards are used to perform visual or spectrophotometric comparisons of bacterial densities in water, saline or liquid growth medium. But for me..in my own version of course, McFarland is to determine the number of bacteria will be standardized for the whole plates. Okay easy~~
Let me tell you about the procedures of making McFarland standard which taught by post-graduate student, Bro Hasan to our group's members.

First portion (1st):
1% of Sulfuric acid added with broth (depending of what type of microorganism that you're using)
e.g. : 1ml Sulfuric acid + Mueller-Hinton broth (technique: put a little bit of broth inside volumetric flask before adding sulfuric acid then add the broth until 100ml)

Second portion (2nd):
1% of Barium chloride added with broth (same as above)
e.g. : 1g of barium chloride added with 100ml of Mueller-Hinton broth.

Mixture:
99.5% of 1st + 0.5% of 2nd
Take 9.95 ml of first portion and add 0.05 ml of second portion.
My technique: Measure 10 ml of 1st in measuring cylinder and pipette out 50 micro-lite from it. Pipette 50 micro-lite of 2nd into the same measuring cylinder. Ta-dah! Standard is complete! What you should do next is just read the absorbent using UV-Vis Spectrophotometry. The wavelength should be according to the journal that you refers to. Like my group, we used 625nm for both bacteria and fungi.

#for bacteria, if you're using MHA, then use MHB. Fungi, if you're using SDA, then use SDB.
* MHA: Mueller-Hinton Agar
   MHB: Mueller-Hinton Broth
   SDA: Sabouroud-Dextrose Agar
   SDB: Sabouroud-Dextrose Broth

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